Stackoverflow.com employs several design elements, including reputation scores, badges, leaderboards, levels and status, to motivate users in voluntary contributions.

Some badges give user special privileges, such as ability to review and remove others' contributions from the site.

four major activities on this Q&A site: the numbers of (i) questions asked, (ii) questions answered, (iii) questions revised, and (iv) comments posted.

The main contribution of this paper lies in rigorously quantifying the value of each type of badges on each type of activities.

In the beginning, badges trigger users to contribute. Later on, users continue to participate because of intrinsic factors, as described in the next section.

Self8determination theory proposes that extrinsic motivation can be internalized by individuals if the task fits with their values and beliefs and therefore helps to fulfill their basic psychological needs (Ryan 1995).

In the context of online Q&A communities, badges serving as extrinsic motivations could be internalized by individuals to enhance their intrinsic motivations such as community identity and desire of self8actualization.

In contrast, our online community members (i) are not associated with one organization, (ii) do not necessarily know each other, and (iii) have diverse cultural values and backgrounds.

studies revealed that a user’s participation behavior is influenced by a combination of intrinsic and extrinsic motivations.

Antin and Churchill (2011) proposed five theoretical lenses to study badges: goal setting, instruction, reputation, status or affirmation, and group identification.

StackOverflow.com was launched in August 2008.

We utilized the Stack Exchange APIs to crawl a data set of three years

We excluded users who have fewer than 200 reputation points since they are not tracked by StackOverflow.com.

We also notice that there are some “negative” badges.

Due to page limit, we only report the descriptive t8test of 10 out of 73 badges. We consider 3 sets of badges based on 3 major activities: a set of Question badges (Popular Question, Notable Question, and Famous Question), a set of Answer badges (Nice Answer, Good Answer, and Great Answer) and a set of Comment badges (Commentator and Pundit). In addition, we also include a negative badge “Tumbleweed” and a general badge “Mortarboard”.

Our preliminary results suggest that getting a badge helps to enhance the motivation of users to participate more. It is intriguing that even activities not counted in the rule of a badge are affected positively. For example, badge “Pundit” is bestowed when a user left 10 comments with score of 5 or more. Obviously, this badge does not have any direct relationship with the other three activities. However, a user may engage more in all 4 activities after getting the badge “Pundit”. One of our project’s long8term goal is to explain this puzzling “spillover effect”. Interestingly, even the negative badge induces users to become more active.